Combined window heater and antenna

ABSTRACT

A heater grid and antenna for defogging a window such as the windshield of an automobile comprises a plurality of resistive conductors and bus bands for the supply of heating current thereto, at least one of said bus bands having an extension beyond its connection to said resistive conductors, by means of which the resistive conductors and bus bands may be tuned for improved radio reception in the frequency modulation band.

United States Patent Sauer 1 Dec. 23, 1975 1 1 COMBINED WINDOW HEATERAND 3,409,759 11/1968 Boicey 6t a1. 219/522 ANTENNA 3,484,583 12/1969Shaw, Jr. 219/522 1 3,484,584 12/1969 Shaw, Jr. 219/522 Inventor: GerdSauer, Aachen-Laurensberg, 3,636,311 1/1972 Steger 219/522 Germany3,778,898 12/1973 Gruss eta1.... 29/611 1731 AS89199 1- 1119118919,311351353 511332 2313151311 33111:: iii/iii Neullly-sur-seme, France3,794,809 2/1974 Beck et al 219/203 22 Filed: May 20 974 3,813,5195/1974 Jochim et a1. 219/522 [21] Appl' Primary Examiner-Volodymyr Y.Mayewsky Attorney, Agent, or Firm-Pennie & Edmonds [30] ForeignApplication Priority Data Oct. 31, 1973 France 7338767 [57] ABSTRACT Aheater grid and antenna for defogging a window [52] 219/522 219/203 5such as the windshield of an automobile comprises a 51 I t Cl 2 0 43/704plurality of resistive conductors and bus bands for the d H 5B supply ofheating current thereto, at least one of said 1 0 are 9/203 bus bandshaving an extension beyond its connection 144/134 343/704 338/309 tosaid resistive conductors, by means of which the re- 56 R f ed sistiveconductors and bus bands may be tuned for iml e erences It proved radioreception in the frequency modulation UNITED STATES PATENTS b 3,366,7771/1968 Brittan et a1 219/522 3,379,859 4/1968 Marriott 219/522 2 Clams 3D'awmg US. Patent Dec.23, 1975 Sheet10f2 3,928,748

Fig. 1

UiS. Patent Dec. 23, 1975 Sheet 2 of2 3,928,748

COMBINED WINDOW HEATER AND ANTENNA The present invention pertains to aheating grid for the windows of automotive vehicles which is capable offunctioning as an antenna for the reception of radio signals, theresistive conductors which make up the heating grid performing asconductive elements of an antenna.

It has already been proposed to employ such grids as antennas, as forexample in US. Pat. Nos. 3,484,583 and 3,484,584. According to one suchprior art construction, there is disposed on an exterior surface of awindshield, comprising a single sheet of glass, a series of narrowhorizontal or vertical conducting resistive strips which are fed attheir two ends through bus bands with heating current, typically directcurrent from the storage battery of the vehicle. In another prior artproposal, the resistive conductors are disposed parallel to each otherand take the form of fine wires having a diameter of 0.005 to 0.05millimeters and these are embedded in the plastic interlayer of athree-layer safety glass, parallel to the upper and lower edges of thewindow. Such embodiments can be used in Windshields as well as in rearwindows since they do not interfere with the drivers vision. I

The heating grids of the type hereinabove described are generally of lowefficiency when employed as antennas for the reception of frequencymodulated signals. The shape of the conductors imposed on them by theirheating function and by the dimensions of the window customarilypreculde their being tuned for optimum performance in the frequencymodulation band. If it is desired to effect such tuning in windows ofthis type, it has been necessary to employ additional circuit elementsexterior of the window. This is inconvenient and moreover does notalways produce satisfactory results.

The present invention provides a window of this type with improvedperformance in the reception of frequency modulated radio signalswithout the necessity for auxiliary exterior circuit elements. Thisresult is obtained, according to the invention, by moving the radio Wavereceiving conductors toward the middle of the window outside theinfluence of the metal parts of the automobile body which surround thewindow and by extending the bus bands beyond or outside the zone of theheating grid conductors, thus making it possible to tune the system inthe frequency modulation band.

In comparison with known constructions, the window of the inventionpossesses important advantages in that it is no longer necessary to haverecourse to auxiliary, exterior circuit elements to obtain an antennatuned to the frequencies which it is expected to receive.

Spacing of the antenna conductors so as to minimize the influence of thevehicle body reduces the capacity of the antenna. In practice, it isnecessary for the antenna to have a capacity below a certain limit. Thatcapacity should not exceed 100 picofarads. This cannot be achieved whenthe antenna conductors are close to the vehicle body. It is thennecessary to reduce capacity of the antenna by the use of exteriorcircuit elements, which further reduces the level of the antenna outputsignal.

Moreover, the solution proposed by the invention for increasing thespacing of the antenna conductor from the vehicle bodies reduces theeffect of perturbating voltages from the latter.

In one embodiment of the invention the two bus bands (e.g. lowresistance conducting strips) by means of which current is fed to theheating conductors are parallel to the side edges of the window and atleast one of these bus bars includes extensions along the edges of thewindow but outside the range of influence of the vehicle body.

In another embodiment of the invention, the bus bands are respectivelyparallel to the upper and lower edges of the window. The lower bus bandincludes extensions or elongations which serve to tune the antenna;these elongations may at their extremities ex tend upwardly parallel tothe side edges of the window.

Since the antenna circuit is used to heat the windshield, the supply ofcurrent thereto requires two leads. Such leads are however a source ofdifficulty, especially at the high frequencies which are involved,because they increase the capacity of the antenna, because they tend tointroduce perturbating voltages from the vehicle body, and because theycomplicate the manufacturing and assembly processes.

It is possible to mitigate these short-comings by disconnecting theleads for supply of heating current when the heating grid is to be usedexclusively as an antenna. A better solution resides in locating the twoterminals for feed of heater current at the same location, in accordancewith one feature of the invention. To this end it is advantageous todivide one of the bus bands into two segments and thereby to divide theheating conductors into two groups which are fed in series. Theterminals for supply of heating current are then connected to the twohalves of this bus band on opposite sides of the break therein. Theantenna signal lead to the receiver is then short-circuited, for radiofrequency voltages, to the heater grid, with isolation from the heatingcurrent being provided by means of capacitors.

A substantial improvement in the antenna performance may then beobtained by disposing the conductors thereof in an asymmetric way withrespect to the vehicle body. Thus it is possible to give unlike lengthsto the two parts of the bus band above referred to by means of whichconnection is made to the radio receiver and to at least one terminal ofthe source of heating current. i

The invention is applicable to windows comprising a single sheet ofglass onto which the conductors are applied in the form of a suspensionof finely divided metallic particles with a binder in a ceramic frit,the suspension being thereafter baked in place. Alternatively theconductors may be laid down in the form of .a conductive coating, forexample of tin oxide. The

invention is also advantageously applicable to laminated Windshields inwhich when conducting wires are disposed in the plastic interlayerbetween inner and outer glass sheets.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be furtherdescribed in terms of a number of presently preferred embodiments and byreference to the accompanying drawings in which:

FIG. 1 is a combined diagrammatic and elevational view of an embodimentof the invention as applied to the windshield of a motor car;

FIG. 2 is a view similar to that of FIG. 1 but showing the applicationof the conducting grid to the rear window of the vehicle; and

FIG. 3 is an elevational view of a third form of combined heater andwindshield antenna in accordance with the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS FIG. 1 shows a safetyglass windshield comprising two glass sheets assembled together with anintervening layer of polyvinyl butyral in which is embedded a grid ornetwork of conductors. This includes in particular parallel verticalconductors 2 connected to an upper bus band 3 and the lower bus banddivided into two parts 4 and 5. The vertical conductors 2 may have adiameter of the order of 0.01 mm. and may have a wavy shape, beingspaced one or two millimeters apart. The bus bands 3, 4 and 5 may have awidth of the order of 3 to 5 mm. and may take the form of silver stripselectrically connecting to the vertical wires 2. The bus bands 4 and 5connect to leads 6 and 7 through a notch 8 formed in the edge of thesheet of glass facing the inside of the vehicle, in order to preventpenetration of humidity between the laminations of the windshield. Thisnotch 8 extends beyond the channel-shaped rubber mounting (not shown)which supports the windshield, so that the leads 6 and 7 do not touchthis mounting. Instead of passing out through a marginal notch, theconductors for supply of heating current may alternatively pass outthrough a hole extending through one of the glass sheets at a shortdistance from the edge thereof, for example as described in thecopending application Ser. No. 334,611 assigned to the assignee hereof.

In the embodiment illustrated in FIG. 1, the resistance wires 2 whichmake up the heating grid comprise two groups of conductors, theconductors of each group being geometrically parallel to the conductorsof the other group and the two groups being connected electrically inseries by means of the upper bus band 3. The bus band 3 may be some fivecentimeters down from the upper edge of the windshield. The lower busbands 4 and 5 may be about 8 centimeters above the lower edge of thewindshield. The portions 4 and 5 of the lower bus band are extendedbeyond the area of the heating conductors 2 at extensions 9 and 10. Thebus bands may be blackened or otherwise rendered nonreflective of lightso as to diminish interference with the drivers vision.

The connections of the heater grid-antenna to the source of heatingcurrent and to the radio receiver will be described below. They aredesigned to connect the conductors 6 and 7 to a common antenna lead byshortcircuiting them together for AC voltages derived from the radiowaves but not for the heating current. The end portions 9 and 10 of thebus band sections 4 and 5 make it possible to tune the antenna for FMreception and to correct its directional properties.

The area occupied by the resistance wires 2 need not be symmetricallydisposed on the windshield. The asymmetric location represented in FIG.1 makes it possible to concentrate the heating effect in that portion ofthe windshield of primary interest, in front of the driver of thevehicle. Moreover it makes it possible to improve the receptioncharacteristics of the windshield and especially its directionalproperties. Such improvement in directional properties may be effectedin part by adjusting the length of the extensions 9 and 10.

Contacts 11 and 12 of the relay 13 control energization of the heatingcircuit. One lead 32 for the heating current connects to ground throughan inductance coil 14. A second lead 33 connects to the ungrounded sideof a battery 37 through an inductance coil 15 and through a resistor 44.These coils have a negligible resistance for direct current, but blockthe passage of the high frequency radio signals captured by the antenna.It is possible to dimension these coils in such fashion as to make themeffective in blocking the frequencies of amplitude modulated (AM) radiobroadcasts (of the order of one megacycle) as well as effective to blockthe frequencies (of the order of one hundred megacycles) employed in thebroadcast of frequency modulated (FM) signals, so as to make it possibleto receive either AM or FM signals during the heating operation. Sincehowever the heating current may amount to 15 amperes this would requirefor these coils such size as to make them unsuitable or excessivelycostly in motor vehicles. If instead their inductance is limited to 4.7microhenries, their impedance will amount to about 3000 ohms at I00megacycles, sufficient to make them operate effectively as filters forfrequency modulation signals only, i.e. to block the passage of FMsignals to ground.

The normal condition of the apparatus, indicated in FIG. 1, is with theheater circuit deenergized. Relay 13 is then deenergized, with itscontacts in the position shown, in which the leads 6 and 7 are isolatedfor all frequencies, including DC, from the battery leads 32 and 33. Theleads 6 and 7 are instead conductively shortcircuited to each other sothat the entire circuit on the windshield feeds the receiver 16 withradio frequency signals through a cable, advantageously of coaxial type,having a center conductor 17. The antenna is then capable of receivingAM as well as FM signals.

When a manually operable contact 18 is closed to energize relay 13 withbattery voltage so as to apply that voltage to the conductors 2 forheating purposes, the conductors 6 and 7 connect to the receiver 16 onlythrough capacitors 19 and 20, which prevent short-circuiting of batteryby the receiver lead 17. The capacity of each of these capacitors is ofthe order of 1000 picofarads so that their impedance does not exceed 1.6ohms at megacycles. This is sufficiently low to constitute an effectiveshort-circuit between the receiver and the antenna for frequencymodulated signals in the frequency modulation band which is in thevicinity of 100 megacycles. The indicator lamp 21 shows that the heatingcircuit is energized.

FIG. 2 shows a construction according to the invention for the rearwindow of an automobile. It comprises a single sheet of glass on whichthere has been deposited by the silk screen process and subsequentlybaked a network of resistive conductors made up of metallic particles inenamel. The heating grid comprises the two vertical bus bands 25 and 26between which are connected horizontal resistive conductors 27. Theauxiliary conductors 28 and 29 connected to the bus band 25 serve fortuning the antenna. Their length is such that the assembly of conductorson the window consti tutes a resonant circuit. The distance from theconductors 25 and 26 to the edges of the glass is of the order of 5centimeters.

In the embodiment illustrated in FIG. 2, the two heating current supplyconductors or leads 30 and 31 are disposed at opposite sides of thewindow. For operation .of the heating circuit of FIG. 2 as an antenna, a

relay such as that described in connection with FIG. 1 is necessary toconnect and disconnect each of these leads.

FIG. 3 represents another embodiment of the invention in which theheating circuit takes the form of two conducting areas 35 and 36covering a large part of the window. These may take the form of thintransparent layers of a metal or of a semiconductor such as tin oxide.Or they may be made up of electrically conducting sheets interposedbetween the two sheets of glass as described in the German publishedapplication No. 1,704,619. The two conductors 35 and 36 are connected inseries by a bus band 37. The two segments 38 and 39 of the lower busband serve for supply of the heating current and also for tuning of theantenna. This tuning is effected as hereinabove described with the aidof extensions 40 and 41, which in the embodiment illustrated extendfirst horizontally beyond the limit of the conducting areas 35 and 36and then upwardly in directions generally parallel to the side edges ofthe window. The conductors 42 and 43 correspond to the conductors 6 and7 of FIG. 1 and are connected to the radio receiver as described inconnection with FIG. 1.

The invention thus provides a window comprising a sheet of transparentmaterial such as the sheet 1 of FIG. 1, usually of glass, a plurality ofelectrically conductive resistive heating conductors such as theconductors 2, 27, 35 and 36 of FIGS. 1, 2 and 3 supported on the sheetand spanning an area thereon smaller than the surface of said sheet, andat least two bus bands such as the bands 3, 4 and 5 of FIG. 1 supportedon the sheet and connecting to the conductors, at least one of the busbands including portions such as the portions 9 and 10 of FIG. 1, 28 and29 of FIG. 2 and 40 and 41 ofFIG. 3 extending beyond that area.

The bus bands may extend substantially parallel to the side edges of thesheet as in FIG. 2, the bus band 25 including at each end an extension(the extensions 28 and 29) substantially parallel to the upper and loweredges of the sheet and outside the zone of influence of a vehicle bodyin which the sheet may be mounted. The bus bands may however extendsubstantially parallel to the upper and lower edges of the sheet, as inFIGS. 1 and 3, with the portions 40 and 41 extending substantiallyparallel to the side edges of the sheet. The conductors 4 and 5 of FIG.1 may be regarded as one bus band divided into two substantiallycollinear parts 4 and 5 each connecting with separate ones of the heating conductors 2, the window further including two terminals for theleads 6 and 7 at adjacent points on those two parts, whereas the busband 3 connects to all of the heating conductors.

The heating conductors such as those illustrated at 2 and 27 maycomprise a suspension of metallic particles in a frit baked on thesurface of the sheet. The bus bands and heating conductors may bothcomprise a suspension of metallic particles in a frit applied to asurface of the sheet by a silk screen process and baked to the sheet.The window may be of laminated construction, comprising a sheet oftransparent plastic adhered to and between two sheets of glass, with theheating conductors taking the form of wires disposed in the plasticsheet. The bus bands are desirably disposed at least 5 centimeters fromthe edge of said sheet, and the parts such as 4 and 5 of FIG. 1 and 28and 29 of FIG. 2 (though the latter are not so illustrated), may be ofunequal length.

The invention also provides a window heating circuit comprising a sheetof transparent material, a plurality of resistive heating conductorssupported on the sheet and spanning an area thereon smaller than thesurface of the sheet, at least two bus bands supported on the sheet andconnecting to those conductors, at least one of the bus bands extendingbeyond that area, two leads such as the leads 6 and 7 of FIG. 1connecting to separate ones of the bus bands, separate capacitors suchas the capacitors l9 and 20 coupling those leads to a transmission linesuch as a coaxial transmission line of which the center conductor isshown at 17 in FIG. 1, and switch means such as the relay 13 with itscontacts 11 and 12 for connecting those leads to a source of voltagesuch as a battery 37.

The circuit may further include inductive means such as the coils 14 and15 interposed between each of those leads and the voltage source.According to a further feature of the invention those inductive meanspossess an impedance low compared to that of the transmission line forfrequencies of the order of one megacycle per second and an impedancehigh compared to that of the transmission line for frequencies of theorder of one hundred megacycles per second. The consequence of thisfeature of construction is that radio signals of frequencies of theorder of one hundred megacycles captured by the heating conductors areeffectively delivered to the transmission line and thereby to a radioreceiver despite connection of the leads to the voltage source by theswitch means, whereas radio signals of frequencies of the order of onemegacycle will be effectively delivered to the transmission line onlywhen the switch means disconnect the leads to the heating conductorsfrom the voltage source.

While the invention has been described hereinabove in terms of a numberof presently preferred exemplary embodiments thereof, the inventionitself is not limited thereto but rather comprehends all modificationsof and departures from those embodiments properly falling within thespirit and scope of the appended claims.

I claim:

1. A windshield for automotive vehicles having a combined heater gridfor heating said windshield at least within an area over which it isdisposed and antenna for reception of frequency modulated radio signalsof a frequency of the order of megacycles, said windshield comprising atransparent substantially rectangular sheet, a plurality of electricallyconductive resistive heating conductors supported on a surface of thesheet substantially parallel to one dimension thereof and spanning saidarea thereon smaller than but constituting a major fraction of thesurface of said sheet, and three bus bands likewise supported on saidsheet and extending at least in part substantially parallel to the otherdimension of said sheet, two of said bus bands being in spaced apartcollinear relation and together with the other bus band connecting saidconductors into a two-terminal circuit comprising said bus bands andconductors, each of said collinear bus bands including a portionextending beyond said area partly substantially collinearly with saidbus band from which it extends and parallel to said other dimension andpartly substantially parallel to said one dimension, said portionshaving a length substantially of the same order of magnitude as eitherof said dimensions, whereby said circuit may be tuned for the receptionof frequency modulated signals of frequencies of the order of 100megacycles, all parts of said combined heater grid and 7 antenna beingspaced from the edge of said sheet sufficien'tly to be outside the zoneof influence of a vehicle body surrounding said sheet.

2. A window for automotive vehicles having a combined heater grid forheating said window at least within an area over which it is disposedand antenna for reception of frequency modulated radio signals of afrequency of the order of 100 megacycles, said window comprising atransparent substantially rectangular sheet, a plurality of electricallyconductive resistive heating conductors supported on a surface of thesheet substantially parallel to one dimension thereof and spanning saidarea thereon smaller than but constituting a major fraction of thesurface of said sheet, and two bus bands likewise supported on saidsheet and extending at least in part substantially parallel to the 8other dimension of said sheet, said bus bands connecting said conductorsinto a two-terminal circuit comprising said bus bands and conductors,one of said bus bands including portions extending beyond said areapartly substantially collinearly with said bus band and parallel to saidother dimension and partly substantially sheet.

1. A windshield for automotive vehicles having a combined heater gridfor heating said windshield at least within an area over which it isdisposed and antenna for reception of frequency modulated radio signalsof a frequency of the order of 100 megacycles, said windshieldcomprising a transparent substantially rectangular sheet, a plurality ofelectrically conductive resistive heating conductors supported on asurface of the sheet substantially parallel to one dimension thereof andspanning said area thereon smaller than but constituting a majorfraction of the surface of said sheet, and three bus bands likewisesupported on said sheet and extending at least in part substantiallyparallel to the other dimension of said sheet, two of said bus bandsbeing in spaced apart collinear relation and together with the other busband connecting said conductors into a two-terminal circuit comprisingsaid bus bands and conductors, each of said collinear bus bandsincluding a portion extending beyond said area partly substantiallycollinearly with said bus band from which it extends and parallel tosaid other dimension and partly substantially parallel to said onedimension, said portions having a length substantially of the same orderof magnitude as either of said dimensions, whereby said circuit may betuned for the reception of frequency modulated signals of frequencies ofthe order of 100 megacycles, all parts of said combined heater grid andantenna being spaced from the edge of said sheet sufficiently to beoutside the zone of influence of a vehicle body surrounding said sheet.2. A window for automotive vehicles having a combined heater grid forheating said window at least within an area over which it is disposedand antenna for reception of frequency modulated radio signals of afrequency of the order of 100 megacycles, said window comprising atransparent substantially rectangular sheet, a plurality of electricallyconductive resistive heating conductors supported on a surface of thesheet substantially parallel to one dimension thereof and spanning saidarea thereon smaller than but constituting a major fraction of thesurface of said sheet, and two bus bands likewise supported on saidsheet and extending at least in part substantially parallel to the otherdimension of said sheet, said bus bands connecting said conductors intoa two-terminal circuit comprising said bus bands and conductors, one ofsaid bus bands including portions extending beyond said area partlysubstantially collinearly with said bus band and parallel to said otherdimension and partly substantially parallel to said one dimension, saidportions having a length substantially of the same order of magnitude aseither of said dimensions, whereby said circuit may be tuned for thereception of frequency modulated signals of frequencies of the order of100 megacycles, all parts of said combined heater grid and antenna beingspaced from the edge of said sheet sufficiently to be outside the zoneof influence of a vehicle body surrounding said sheet.